The present invention relates to a reactor containment vessel containing a reactor pressure vessel, and more particularly, to a reactor pressure vessel supporting pedestal having an improved structure.
Generally, as shown in FIG. 7, a reactor primary containment vessel (PCV) 1 contains a reactor pressure vessel (RPV) 2. The PCV 1 is composed of an outer wall structure W, in the inside of which an upper drywell 5 is formed and a lower drywell 7 is also formed below the upper dry well 7. A suppression chamber 8 for absorbing steam energy discharged in the upper and lower dry wells 5 and 7 at a reactor accident is formed inside the wall structure W. In the upper drywell 5, the RPV 2, a line 3 connected to the RPV 2 and an air conditioning system 4 are disposed, and in the lower drywell 7, a control rod driving mechanism 6 and others are disposed.
The RPV 2 is supported by a pedestal 12 which is supported at one end by the outer wall structure W through a diaphragm floor 22 and has a cylindrical structure surrounding the RPV 2. A line 9, a cable 10 and a duct 11 are also arranged in the upper and lower drywells 5 and 7, and a connecting vent 13 is formed to the pedestal 12 to pass the line 9, the cable 10 and the duct 11. In an actual design, a plurality of these line, cable and duct may be arranged, but in the illustration, only the cables 10 are shown as plural. This connecting vent 13 serves as a flow passage for guiding the steam discharged from the line, which is broken in an reactor accident, into a vent pipe 14 which is disposed at the lower portion of the pedestal 12. The steam is then guided into the suppression chamber 8 in which the steam is condensed as a suppression pool water 25.
In such accident, since non-condensable gas such as nitrogen gas is also flown into the suppression chamber 8 as well as the steam, the pressure inside the suppression chamber 8 increases.
Upon breaking the line or duct, the pressure inside the upper and lower drywells 5 and 7 also increase. However, coolant is supplied through a core cooling system at such emergency, and when the broken portion of the line or duct is filled up with the coolant, the steam in the upper and lower dry wells 5 and 7 are condensed as suppression pool water 25, thus rapidly decreasing the pressure inside the drywells 5 and 7. When the pressure inside the drywells 5 and 7 is rapidly lowered, a pressure load is severely applied to the diaphragm floor 22 formed as a partition wall sectioning the upper and lower drywells 5 and 7. In order to prevent such pressure load from appling to the diaphragm floor 22, vacuum breakers 24 are mounted to the pedestal by means of mounting or fixingpipes 23, respectively, as shown in FIGS. 9 and 10. Namely, when a difference in pressures inside the upper drywell 5 and the lower drywell 7 exceeds a predetermined value, the vacuum breakers 24 are operated to flow the gas inside the lower drywell 7 into the suppression chamber 8. These vacuum breakers 24 are disposed in plural numbers along the circumferential direction of the pedestal 12 as shown in FIG. 10.
Generally, in the PCV 1, a plurality of internal pumps are arranged inside the PCV 1 along a circumferential direction of a reactor core disposed in the RPV 2 with predetermined spaces with each other and a plurality of vent pipes 14 are also arranged along the circumferential direction of the RPV 2 generally at positions corresponding to the internal pumps.
Namely, as shown in FIG. 8, the pedestal 12 is sectioned into a plurality of the connecting vents or passages 13 and a plurality of concrete wall sections 12a, which are alternately arranged along the circumferential direction of the pedestal 12. The pedestal 12 is lined by steel plates, for example, and accordingly, each of the connecting vents 13 is defined by the adjacent concrete sections 12a and the inner and outer steel plates.
In such arrangement, however, as shown in FIG. 8 shown as sectional view taken along the lines VIII--VIII in FIG. 7, the line 9, the cables 10, the duct 11 and other elements are disposed in the connecting vent 13 above each of the vent pipe 14, so that it is difficult to ensure a sufficient steam flow area for the vent pipe 14 at a time of accident of the reactor.
Moreover, as shown in FIG. 9 or 10, the fixing pipe 23 to which the vacuum breaker 24 is secured penetrates the connecting vent 13 above the vent pipe 14, so that the location of the vacuum breaker 24 and the fixing pipe 23 is complicated, thus being disadvantageous.